Precision measurement of the electromagnetic fields in the focal region of a high-numerical-aperture lens using a tapered fiber probe

Rhodes, S.; Nugent, Keith A.; Roberts, Ann

doi:10.1364/josaa.19.001689

Cited by 32 publications

(19 citation statements)

References 18 publications

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“…As suggested previously by several workers [11,35,106,107], the X polarised intensity PSF has a 2-fold rotational asymmetry. Another important result is the non-zero Z polarised intensity PSF, whose peak value is as high as 15% of the X polarised PSF peak intensity for the lens considered here.…”

Section: Focal Field Structure Of a Linearly Polarised Beamsupporting

confidence: 65%

Programmable diffractive optics for laser scanning confocal microscopy

Boruah

Neil

2007

SPIE Proceedings

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Coherent light beams find applications in several exciting research areas where it is important to have absolute control over the phase and amplitude properties of the light beams.To name a few, in applications such as microscopy, optical trapping, interferometry etc. it is imperative to have dynamic control over the properties of the beam. One way of achieving this is with the help of a computer controlled diffractive optical element such as a liquid crystal spatial light modulator (LCSLM). Based on the principle of holography, such a technique can provide dynamic control over amplitude, phase and polarisation state across a coherent beam.This work describes about a ferro-electric liquid crystal spatial light modulator (FLC-SLM) system acting as a programmable diffractive optical element. The efficiency of the system to detect and correct aberrations in laser beams were demonstrated. The ultra sensitivity of singular light beams to the presence of azimuthal aberrations were observed and a novel aberration sensor based on these findings were implemented. The synchronisation of the display holograms on the FLCSLM panel with the acquisition of a CCD camera is demonstrated in a programmable reference beam phase stepping interferometry experiment.Laser scanning confocal microscopy is a widely used technique for the electronic visualization of optically sectioned microscopic structures. The information available from such a system is limited by the intensity and polarisation properties of the point spread function (PSF) at the sample plane, which are in turn dependent on the optical system and the sample being imaged. Aberrations due to incorrect optics or the sample itself may significantly degrade the PSF there by reducing the resolution and the signal available for image formation. Also the information obtained from a laser scanning confocal system working in the epi-fluorescence mode will also depend on the polarisation properties of the PSF, as molecular absorption and emission cross-sections are polarisation dependant. These polarisation properties can be particularly important for high resolution microscopy such as STED and molecular alignment studies when high numerical aperture lenses are used that can result in complex polarisation structure within the PSF. The thesis develops the theory necessary to understand the vectorial behaviour of the 3D PSF for an arbitrarily polarised beam. The design and implementation of a beam scanning optical microscope system, that uses an FLCSLM to control the optical field in the illumination pupil of the microscope objective, are described. The performance of the system in engineering and reconfiguring the 3D PSF is demonstrated. Use of programmable diffractive optics to generate different depletion beams for STED microscopy is also demonstrated. 2To My Parents 3

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Section: Focal Field Structure Of a Linearly Polarised Beamsupporting

confidence: 65%

Programmable diffractive optics for laser scanning confocal microscopy

Boruah

Neil

2007

SPIE Proceedings

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“…In this case, polarization effects can be seen if the detection angle is sufficiently large. As an alternative to provide for the necessary high numerical aperture detection, a scanning near field optical microscope ͑SNOM͒ fiber tip 10 can also be used. In principle, it is even possible to measure phase and amplitude with a SNOM, 11 however, the sensitivity for longitudinal and transverse components can differ 12 and this discrepancy needs to be taken into account for the interpretation of the results.…”

Section: Introductionmentioning

confidence: 99%

Using a quantum well heterostructure to study the longitudinal and transverse electric field components of a strongly focused laser beam

Rurimo

Schardt

Quabis

et al. 2006

Journal of Applied Physics

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We report a method to measure the electric energy density of longitudinal and transverse electric field components of strongly focused polarized laser beams. We used a quantum well photodetector and exploited the polarization dependent optical transitions of light holes and heavy holes to probe the electric field distribution in the focal region. A comparison of the measured photocurrent spectra for radially and azimuthally polarized beams at the light and heavy hole absorption peaks provides a measure of the amount of the longitudinal electric field component.

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“…However, due to the limitation of the resolving power of a camera, the measurement of focusing spot was realized only for low NA (0.01) OL, in which the polarization effect of the incident beam is not significant, resulting in a symmetric intensity distribution in its focal plane. Using a tapered fiber probe 16 with a tip aperture diameter between 50 and 100 nm, it is possible to map the asymmetric EM distribution of a tightly focused beam with good spatial resolution. However, the probe tip displays unequal sensitivity to the different components of EM field that might affect the reconstructed shape of focusing spot.…”

Section: Introductionmentioning

confidence: 99%